Hi, Eric!
On Feb 19, Eric Jensen wrote:
> On Feb 19, 2009, at 2:33 AM, Sergei Golubchik wrote:
>> On Feb 18, Eric Jensen wrote:
>>
>> You want to create a temporary table with a btree index, put all union
>> data into it, and then retrieve rows in the index order ?
>
> No, not all union data, only the rows necessary for performing the merge,
> using the index to select the next top value that determines which
> component select to read a new row from next.
Ah! Okay, now I understand.
> 4. make st_select_lex_unit::exec use k-way merge logic relying on this
> one-result-at-a-time fetching to retrive up to LIMIT n results
> treating our temp table with its ordered index as a heap
Wouldn't it be better to use a heap as a heap, not btree as a heap ?
Heap is faster than btree, and MySQL has a heap implementation in
mysys/queues.c
Regards / Mit vielen Grüßen,
Sergei
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